CHG: Make world grid limits not limited to height of water. Steps up savegame version.

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6392 8aca7d54-2c30-db11-9de9-000461428c89
FIX: A typo I made caused the display routine to check more tiles than it really needed.

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6393 8aca7d54-2c30-db11-9de9-000461428c89